Since Rhode Island health officials reported a cluster of fatal overdoses of fentanyl, in spring 2013, the drug has replaced prescription painkillers and heroin as the chief driver of the nation’s opioid crisis.

In New Hampshire, fentanyl has been implicated in at least 789 deaths since 2014, or two of every three fatal overdoses. Here are four reasons why New Hampshire’s opioid epidemic is now a fentanyl crisis.

1. Chinese Connection

Prescription fentanyl, most often used to used to treat severe cancer and post-surgical pain, accounts for a very small portion of the drug’s black market, according to the Drug Enforcement Administration. And while an epidemic of illicit fentanyl in the mid-2000s was traced to a single clandestine lab in Mexico, the current crisis originates in China, the world’s largest manufacturer of pharmaceutical ingredients.

Weakly regulated drug manufacturers export precursor chemicals to Mexico and Canada, where they are used to make fentanyl analogues, compounds that have a slightly different chemical structure than the pharmaceutical version. The analogue is then cut and mixed with other drugs or non-psychoactive “fillers” like baby laxative before it’s sold on the street.

Analogues can be many times more potent than pharmaceutical fentanyl, which is up to 50 times stronger than heroin. A fatal dose of fentanyl is minuscule, about 2 milligrams, compared to heroin, so it’s much more profitable.

The DEA estimates that a kilogram of heroin costs $6,000-$7,000 and can produce $80,000 in sales on the street. A kilogram of a fentanyl analogue costs less than $5,000 and is so potent it can be cut and processed into as many as two dozen kilos, generating $1.5 million to $2 million in profit.

Moreover, trafficking in fentanyl analogues doesn’t require a great deal of upfront cost or expertise. The precursor chemicals and equipment are relatively inexpensive and easily purchased online via the “Dark Net,” and English-language websites in China virtually guarantee shipments will arrive without detection by law enforcement.

3. Emerging Markets

Fentanyl analogues are traditionally cut with heroin, but the enormous profit margins, combined with the country’s high rates of prescription painkillers use, are driving traffickers to create new formulations.

Fentanyl is also turning up in counterfeit non-opioid medications. After several reports of deaths from counterfeit Xanax in 2015 and 2016, the DEA issued a report, warning of the presence of fentanyl in a variety of other counterfeit prescription drugs. These versions of fentanyl can be especially dangerous: a lab analysis of one batch of counterfeit pills found doses as small as .6 milligrams of fentanyl and as high as 6.9 milligrams.

“Such wide disparity in dosing,” the report said, “reveals that the producers were likely new to incorporating fentanyl in pill production, as the fentanyl was not thoroughly mixed with the other powders before binding and pressing into pills.”

Perhaps the most telling statistics were related to seizures of the drug by law enforcement. The number of fentanyl shipments intercepted in New Hampshire nearly quadrupled from, 225 in 2014 to 866 in 2015, while the number of heroin seizures decreased 24 percent.

In 2015, the amount of fentanyl intercepted by state and local police and the DEA - roughly 60 pounds - was more than double the amount of heroin seized. The primary source of fentanyl for central and eastern New Hampshire is Lawrence, Ma., while western parts of the state rely on traffickers in Springfield, Ma.

And, according to the report, users are increasingly becoming dealers, who are “fronted” large quantities of fentanyl or heroin from sources in Massachusetts and Connecticut for distribution in small Granite State towns and cities.

Citing intelligence collected law enforcement in the New England High Intensity Drug Trafficking Area, fentanyl and heroin are “a high threat to the region as a result of widespread availability, high incidence of addiction, association to other criminal activities, and negative economic impact.”

For a disturbing window into the world of illicit fentanyl, check out this VICE documentary, told from the perspective of a community of drug users in Canada.